THE BASIC OPE2ST-HEAKTH PROCESS.
CaO over what is necessary to satisfy its own acids./ Two representative limes are assumed in Table XI- C, both containing 80 per cent. CaO,, one with 3 per cent, and the other with 7 per cent. Si02, and the computation is made for two different slags. The pure lime is worth 31 per cent, more than the impure when a calcareous slag is to be formed., but if a more silicious cinder is permissible, as in the case when little phosphorus is to be removed; the pure lime is worth only 12 per cent. more. •
TABLE XI-C. Eelative Values of Limes with 3.0 and 7.0 Per Cent, of Si02.
Slag A. Slag B.
Lime with 8 per cent. SiOa. Lime with 7 per cent. SiOa. Lime with 8 per cent.SfO,. Lime with 7 per cent. SiO,.
12.0 48.0 4.0 80.0 12.0 12.0 48.0 4.0 80.0 20.0 40.0 2.0 80.0 20.0 40.0 2.0 80.0
CaO in slag; per cent ..........
Eatio CaO to 8iO3 in slag .......
Total CaO in lime; per cent ......
CaO in the lime which is needed to satisfy its own silica; per cent. 4.0x8.0 ............
4.0X7.0 ... ...... 23.0
20x80 . 6.0
2.0X7.0 ............. 14.0
CaO available for foreign silica; per cent ... .......... 68.0 1.31 52.0 1.00 74.0 1.12 66.0 1.00
Relative value ..............
SEC. Xlh.—Basic open-hearth slags.—The proportions of Si02 and CaO are the main points in a basic slag, but other factors exercise an important influence upon the result. Magnesia is always present from the wear of the hearth, but is undesirable^ as it makes the slag viscous and has less power to hold phosphorus than lime. Alumina comes from the impurities in the dolomite, lime and ore, but being usually in small amount may be neglected. Manganese is usually present in the stock and serves a useful purpose in conferring fluidity upon the slag. It is also valuable in removing sulphur by the formation of sulphide of manganese, which floats to the top of the metal, where the sulphur, being exposed to the flame, is oxidized and passes away with the waste gases. This action is uncertain, and the explanation is somewhat a matter of supposition, but it seems well proven that manganese, either metallic or in the form of ore, aids in the, elimination of sulphur, and the above